1. Field of the Invention
The present invention relates to a liquid viscosity detecting method for a liquid droplet ejecting device, a control method for a liquid droplet ejecting device, and a liquid droplet ejecting device.
2. Description of the Related Art
Inkjet recording apparatuses using, for example liquid droplet ejecting devices, have been known as image forming apparatuses such as printers, facsimile machines, copiers, multifunction peripherals (MFP), etc. In the inkjet recording apparatuses, inkjet recording heads are adapted to eject ink droplet onto recording media, such as papers or viewgraphs (OHP sheet) to form a desired image. As the inkjet recording head, there is known a piezoelectric type head in which a piezoelectric element is used as a pressure generator element to pressurize the ink in an ink channel to cause a vibration plate that forms a wall of the ink channel to vibrate, which changes a volume of the ink channel to eject ink droplets.
The inkjet recording head is equipped with multiple nozzles to eject ink. Herein, ink viscosities fluctuate among the multiple nozzles, by being affected by change in the circumferential temperature and humidity and affected by self-heat generation during continuous driving. As the ink viscosities are changed among the nozzles, the ejecting speed of the respective nozzles vary, which may cause defective image formation such as image density fluctuation, image partly absent creating white lines, and color tone change. When the ink viscosity is further increased, the nozzle is clogged, the image in which the ink is partly absent creating white dots occurs.
In order to implement correcting and recovering appropriately as a countermeasure to the fluctuation in the ejecting speeds and nozzle clogging, it is necessary to detect the change in the ink viscosity.
Herein, immediately after a drive voltage (drive waveform) is applied, a residual pressure wave in the individual liquid chamber (ink channel) vibrates (residual vibration) the piezoelectric element. During the residual vibration, a counter electromotive force is generated in the piezoelectric element. As a method to detect the change in the ink viscosity, a residual vibration detection technique in which the counter electromotive force of the residual vibration is detected is proposed.
As one example technique, there is a residual vibration detector that is equipped with a residual vibration detection unit including a filter circuit, an amplification circuit, a comparison circuit, a logic circuit and so on; a transistor functioning as a switching element. Immediately after the drive waveform is applied, the piezoelectric element is connected to the residual vibration detection unit by switching the switching element, and the residual vibration detection unit acquires an elapsed period until the drive vibration waveform reaches a reference voltage Vref and a cycle of the residual vibration waveform. Then, an amplitude value is calculated in accordance with the ratio of the vibration cycle to the elapsed period until the residual vibration voltage reaches the predetermined reference voltage Vref, and with a condition that the residual vibration is a sine wave based on the residual vibration waveform. The ink viscosity is detected based on the magnitude of the amplitude values of a first half wave (JP-2011-189655-A).
In this example, the residual vibration waveform is incorporated into the residual vibration detection unit after the switching element is switched, and the amplitude value of the first half-wave is calculated based on the ratio between a cycle of the residual vibration waveform and the elapsed period until the residual vibration waveform reaches the predetermined reference voltage Vref, to detect the ink viscosity. However, variations in the ON-resistance/ON-period of the switching element directly affect the elapsed period until the residual vibration waveform reaches the reference voltage Vref, and accordingly a large variation occurs in the first half-wave amplitude values, so that a small change in the ink viscosity cannot be detected.